1. Field of the Invention
The present invention generally relates to organic electroluminescence. More particularly, the present invention pertains to novel organic compounds having electroluminescent (hereinafter referred to as “EL”) characteristics and an organic EL device using the organic EL compounds.
2. Description of the Related Art
Organic electroluminescence is one of the instances in which electric current is converted into visible light by internal processes of certain organic molecules. Organic molecules having either fluorescent or phosphorescent characteristics generate light emission upon the application of electric current, although they differ in their internal processes and response time. Both organic fluorescent and phosphorescent molecules are referred to as organic EL or light-emitting molecules.
The organic EL technology has been used in luminescent displays which produce their own light, unlike liquid crystal displays, which require an independent light source. Various colors can be generated by using an individual color-generating compound or combining compounds generating basic color elements. This technology is advantageous over LCD technology in its low power consumption, faster response time, higher brightness level, unlimited viewing angle and thinner design.
A basic construction of an organic EL device includes two opposing electrodes, i.e., a cathode and an anode, and an intervening layer containing an organic light-emitting material. When applying an electric voltage between the electrodes, electrons and holes are injected from the cathode and anode, respectively, into the intervening layer. The holes and electrons recombine at organic light-emitting molecules in the intervening layer. Recombined pairs of electrons and holes, namely excitons, move around carrying the energy generated by the recombination and transfer the energy to other organic light-emitting molecules, particularly to those having a smaller band gap near the location of their recombination. The transferred energy is used to excite valence electrons of the organic light-emitting molecules, which generates photons when the electrons return to their ground state.
In order to improve energy efficiency, multiple-layered organic EL devices have been suggested. Generally, multiple-layered organic EL devices have one or more layers functioning as vehicles for hole injection, hole transportation, light emission, electron transportation, and electron injection. One or more layers of the multiple-layered constructions may have more than one function. Many organic compounds have been known to have physical properties and characteristics for use in such organic EL devices. However, there exists a need for new organic compounds for use in organic electroluminescence in order to improve various aspects of organic EL devices or the manufacture of such devices.